Let me trace through the undo logic to make sure it's correct.
When placeTile(x, y, color) is called:
existing = grid[y][x] (could be null or a color)- If
existing === color, return (no change)
- Check if color is available
- Push history:
{x, y, prev: existing, prevColor: existing ? colorCounts[existing] : null, newColor: color, newCount: colorCounts[color]}
- If existing is not null and has a count, increment it (return the old tile)
- Decrement the new color count
- Set grid[y][x] = color
When undo() is called:
- Pop history entry
h
- Set
grid[h.y][h.x] = h.prev (restore old tile or null)
- If
h.prevColor !== null and colorCounts[h.prev] is defined, restore colorCounts[h.prev] = h.prevColor
- This restores the count of the previously placed tile to what it was before the placement
- Wait, but in placeTile, we incremented colorCounts[existing] if it existed. So prevColor should be the count BEFORE the increment.
- Actually, let me re-read:
prevColor: existing ? colorCounts[existing] : null - this captures the count BEFORE the increment.
- Then in undo, we set
colorCounts[h.prev] = h.prevColor which restores it to the pre-increment value. That's correct!
- If
h.newColor exists and colorCounts[h.newColor] is defined, restore colorCounts[h.newColor] = h.newCount
newCount: colorCounts[color] captures the count BEFORE the decrement.- In undo, we restore it. That's correct!
Wait, but there's a subtle issue. In step 3 of undo, we check h.prevColor !== null. But what if h.prev is null (i.e., the cell was empty before)? Then prevColor would be null, and we skip restoring. That's correct because there's nothing to restore.
But what if h.prev is a color but h.prevColor is 0? Then h.prevColor !== null is true (0 !== null), so we'd restore it. That's correct.
Actually wait, there's a potential issue. In placeTile:
If existing is null, prevColor is null. If existing is a color, prevColor is colorCounts[existing] (the count before incrementing).
Then:
This increments the count of the old color (returning it to the pool).
Then:
This decrements the count of the new color (taking it from the pool).
In undo:
This looks correct! The undo properly restores both counts.
For removeTile:
In undo:
grid[h.y][h.x] = h.prev (restore the tile)h.prevColor !== null is true (since existing was not null), so colorCounts[h.prev] = h.prevColor (restore to pre-increment)h.newColor is null, so the second if is skipped
This is correct!
The undo logic looks solid. Let me now do a final check of the game to make sure everything is in order.